rust: Generate per recipe target configuration files

Instead of generating target configuration files centrally and often getting
it wrong, or having trouble finding the right set, generate them dynamically
from the bbclass into WORKDIR per recipe.

(From OE-Core rev: 9160e4a37561d8ac882057450a818621bec13bed)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-devtools/cargo/cargo.inc

@@ -18,6 +18,8 @@ EXCLUDE_FROM_WORLD = "1"
 
 inherit cargo pkgconfig
 
+RUST_TARGETGENS = "BUILD HOST TARGET"
+
 do_cargo_setup_snapshot () {
 	${WORKDIR}/rust-snapshot-components/${CARGO_SNAPSHOT}/install.sh --prefix="${WORKDIR}/${CARGO_SNAPSHOT}" --disable-ldconfig
 	# Need to use uninative's loader if enabled/present since the library paths

meta/recipes-devtools/rust/libstd-rs.inc

@@ -12,6 +12,9 @@ DEPENDS:append:libc-musl = " libunwind"
 DEPENDS:remove:riscv32 = "libunwind"
 DEPENDS:remove:riscv64 = "libunwind"
 
+
+RUST_TARGETGENS = "BUILD HOST TARGET"
+
 # Embed bitcode in order to allow compiling both with and without LTO
 RUSTFLAGS += "-Cembed-bitcode=yes"
 # Needed so cargo can find libbacktrace

meta/recipes-devtools/rust/rust.inc

@@ -12,9 +12,6 @@ DEPENDS:append:class-native = " rust-llvm-native"
 
 S = "${RUSTSRC}"
 
-# We generate local targets, and need to be able to locate them
-export RUST_TARGET_PATH="${WORKDIR}/targets/"
-
 export FORCE_CRATE_HASH="${BB_TASKHASH}"
 
 RUST_ALTERNATE_EXE_PATH ?= "${STAGING_LIBDIR}/llvm-rust/bin/llvm-config"
@@ -40,6 +37,8 @@ setup_cargo_environment () {
 
 inherit rust-target-config
 
+RUST_TARGETGENS = "BUILD HOST TARGET"
+
 do_rust_setup_snapshot () {
     for installer in "${WORKDIR}/rust-snapshot-components/"*"/install.sh"; do
         "${installer}" --prefix="${WORKDIR}/rust-snapshot" --disable-ldconfig